Role of the solitary tract nucleus and caudal ventrolateral medulla in temperature responses in endotoxemic rats

In experiments on conscious rats it was found that preliminary microinjection of 100 nl 100 mu M glutamic acid to the rostral commissural part of the solitary tract nucleus or to the caudal ventrolateral medulla increased a rise in colonic temperature induced by systemically applied endotoxin (3 mu g/kg Escherichia coli lipopolysaccharide, i.p.) as compared to animals with intrabulbar injection of vehicle (control group). Preliminary microinjection of glutamate to the caudal commissural part of the solitary tract nucleus levelled the endotoxin-induced temperature response. After glutamate treatment of the caudal ventrolateral medulla there was a significant decrease in the noradrenaline content and decrease in the adrenaline level in the caudal (not significant) and rostral ventrolateral medulla (significant:), as well as a small rise in noradrenergic activity at the solitary tract nucleus as compared to control animals. The post-mortem measurement of the optical density of brainstem tissues revealed its significant attenuation at the solitary tract nucleus and caudal ventrolateral medulla after glutamate as compared with these structures after vehicle. The involvement of monoaminergic systems of both structures under study in the initiation and control of temperature responses during endotoxemia is suggested.